Non-conventional sol–gel synthesis for the production of boron-alumina catalyst applied to the vapour phase Beckmann rearrangement Original Research Article

In the past few years, vapour phase Beckmann rearrangement of cyclohexanone-oxime to caprolactam has been investigated in depth and a wide variety of catalysts has been studied. To date a large number of experiments concerning non-zeolitic supported boron oxides have been carried out. In the present work, we report on boria-alumina catalysts where the boron is part of the catalyst lattice, these catalysts being tested for the cyclohexanone-oxime vapour phase rearrangement to caprolactam. These catalysts are obtained by the sol–gel route using (NH4)2B4O7 as the source of boron, which has never been used before in B/Al sol–gel synthesis. The local environment of catalysts was characterised by solid state 27Al- and 11B-MAS-NMR and their structure by X-ray powder diffraction; the acidity was determined by TPD of ammonia. The effect of B/Al ratio and the role of different polar agents in the feed were also investigated by catalytic tests.